In the field of catalytic reforming or of aromatic hydrocarbons production, the catalysts with an alumina base, containing, in addition to a noble metal of group VIII (generally platinum), a metal promoter consisting of rhenium (U.S. Pat. No. 3,415,737) are known for their industrial impact. Also the catalysts with a group VIII noble metal base (usually platinum) and containing, as promoter, for example tin or indium or thallium (U.S. Pat. No. 3,700,588 - U.S. Pat. No. 2,814,599) are known to form new races of catalysts.
These catalysts have been tested and used over very long periods, for example of about one year and, whereas the platinum-rhenium catalyst shows an excellent stability, it does not give a maximum selectivity in the production of high grade gasolines. Conversely, platinum-tin, platinum-indium or platinum-thallium catalysts give an excellent selectivity but their stability remains insufficient.
Accordingly, it appeared judicious to use catalysts containing, in addition to platinum, both promoters simultaneously, for example rhenium and tin (U.S. Pat. No. 3,702,294). However, the selectivity obtained by using this type of catalyst was still lower than that obtained with a platinum-tin or platinum-indium or platinum-thallium catalyst and, in addition, this catalyst was also less stable than the platinum-rhenium catalyst.